1. Field of the Invention
The present invention relates to an image reader apparatus, particularly to a small-sized image reader apparatus, e.g., an image scanner, which is capable of taking characters, figures or the like on a document into an information processing apparatus such as a personal computer or a word-processor by manual scanning.
2. Description of Related Art
A conventional hand-scanning image scanner is manually moved on a document such as a newspaper, a book, a magazine, a postcard, a visiting card or the like to read an image thereon.
The image scanner is mainly composed of a light source to illuminate a document, an optical device to form an image of the document to be read, an image sensor to convert the formed image into quantity of electricity, a running roller for smoothly moving a housing of the image scanner on the document and an encoder to detect a rotation angle of the running roller.
Light emitted by the light source linearly illuminates the document through a transparent reading window provided on the housing of the image scanner at a position facing the document. Light reflected from the document passes through the reading window again and is then directed to the optical device to form an image on the image sensor composed of a number of photoelectric converting elements arranged in a row. Data of the image converted to quantity of electricity by the image sensor is then transmitted to an information processing apparatus such as a personal computer, a word-processor or the like. When the image scanner is moved on the document, the amount of movement of the image scanner is detected as the amount of rotation of the running roller. Every time when this amount of movement reaches a value predetermined from a density of scanning, the image data converted to the quantity of electricity is transmitted sequentially.
Here, as the optical device, conventionally used are those of a reduction optical system employing a single pair of lenses as shown in FIG. 12 and those if a contact optical system employing a rod lens array composed of a plurality of microlenses as shown in FIG. 13.
When a document is read by the hand-scanning image scanner, a distance between the optical device and the document may sometimes change because of unintentional movement of a user's hand in operating the image scanner, which movement may move the image scanner away from the document; because of curves of the sheets when opened to expose the page, in the case where the document is a page of bound sheets of paper like a book; and because of wrinkles of the document. In order to cope with such change of the distance between the optical device and the document, most conventional hand-scanning image scanners employ optical devices of the reduction optical system, which have deep depth of focus.
However, since the image scanner having the optical device of the reduction optical system forms a reduced image of the document by the single pair of lenses, the distance between the document and the image sensor is long and the image scanner needs a relatively large housing. Therefore the image scanner of this type has problems in portability and operability. Especially the position of the document is remote from a reading portion of the image scanner, i.e., a center of imaging of the optical device. Accordingly, when a side, top or bottom end part of a book or a bound document is scanned, the housing of the image scanner projects greatly out of the book or the document and it is difficult to read the page with keeping the image scanner horizontal to the document.
In the case of an image scanner having an optical device of the contact optical system, on the other hand, the housing thereof can be reduced in size since the distance between the document and the image sensor is small. However since this optical system has a small depth of focus, the contact optical system is rarely adapted to the manually operated image scanner in which the distance between the optical device and the document may change. As shown in FIG. 14, however, there is known an image scanner having a construction such that the housing of the image scanner is partially formed flat around a reading window, the document is pressed onto this flat part when being scanned so that the distance between the optical device and the document does not change. The roller for detecting the amount of movement of the image scanner is formed outside the flat part with some distance therefrom so that the roller does not prevent the contact of the document with the flat part. In this case, it is preferable that the width W of the flat part is large enough for ensuring stable operation (referring to FIG. 14, the width is about 19 mm), and therefore it is difficult to reduce the distance between the image reading portion and a document contact portion of the roller (referring to FIG. 14, the distance is about 18 mm). As a result, when scanning an side, top or bottom end part of the document, the housing of the image scanner may project out of the document as discussed in the case of the reduction optical system.
When the housing of the image scanner inclines or projects out of the document, on the document like a book, a focal length becomes off and an accurate image of the document cannot be obtained. Besides, in the case of a book, a side of the housing of the image scanner may come in touch with a bound portion of the book and the movement of the image scanner is restricted. As a result, an side end part of the document on the binding side may not be read or may be incompletely read.
Accordingly, in order to read the document completely to peripheral parts, it is necessary to change the position of the document or to change the direction of the housing of the scanner, which will make the operation much complicated. In order to ensure the complete reading of the document without letting the document contact portion of the housing out of the document or changing the position of the housing or the document during operation, the distance between the image reading portion and the document contact portion of the housing should be as short as possible.
Generally, documents read by such a hand-held image scanner include those printed on flat sheets of paper, books, newspapers and the like. Such documents typically have upper, lower, right and left margins of about 10 mm in view of performance of printing machines as well as the cutting of printed sheets.
Though sometimes no margins are provided due to illustrations or the like, important information is rarely printed in peripheral parts of sheets.
Therefore, it is preferable that the distance between the image reading portion and the document contact portion of the housing is as short as possible, but the distance may be set nearly the length of margins without any practical problems because the margins do not need to be read necessarily.